Title: Linkage, Association, and Gene-Expression Analyses Identify CNTNAP2 as an Autism-Susceptibility Gene
Source: The American Journal of Human Genetics 82, 150–159, January 2008
Authors: Maricela Alarcon, Brett S. Abrahams, Jennifer L. Stone, Jacqueline A. Duvall,
Julia V. Perederiy, Jamee M. Bomar, Jonathan Sebat, Michael Wigler, Christa L. Martin,
David H. Ledbetter, Stanley F. Nelson, Rita M. Cantor, and Daniel H. Geschwind.

As probably some of you have seen in the press today, the North American Journal of Behavioral Genetics just published 3 studies linking specific Genes to Autism. I just finished reading all three articles and I can say the results are fascinating (from a research perspective). I will limit this review to the main article “Linkage, Association, and Gene-Expression Analyses Identify CNTNAP2 as an Autism-Susceptibility Gene“ In this large study the researchers explore specific SNIPS (Single nucleotide polymorphism). SNIPS are rare genetic variations that represent our individual differences. That is, SNIPS are the variations in our genetic sequence that makes us different. Why are these important in bio medical research? Because if you can identify specific variations (SNIPS) that are more commonly or uniquely transmitted from one generation to another, and these generations also happen to have a unique disorder, it is possible to assume that the disorder may be affected or even caused by such specific genetic variation.

So this study explored a very rare genetic variation in a specific gene: the CNTNAP2. This is a gene that has been previously related to language delays and believed to play an important role in language development. This study found that a specific variation in the CNTNAP2 gene contribute to variability of “Age at first word” (How old was the child when he/she said the first word) in boys with autism (but not girls!). That is, the groups included in the study consisted of boys and girls with autism who had an average age at first word at around 30 months (typically developing kids say their first words at around 12 month). The researchers found that a particular variation in the CNTNAP2 was most commonly transmitted amongst these boys than amongst the girls or than amongst what is expected if such variation was random (like it is in the general population). The authors mentioned a similar study with Amish families that found this particular gene to be related to the presence of seizures, language delays, and social deficits. They argue that this particular gene may affect the development of ASD during the embryonic phase by affecting the way our brains change during early development. It is interesting to note that a similar process (disruption in normative brain development – specifically the way our cells migrate in our brain) has been proposed as the explanation of the “regressive” variant of autism.This is a variant experienced by many children consisting of normal development up to the age of 2 followed by a rapid regression and loss of abilities.

This is not the first study linking specific SNIPS to ASD, but provides more evidence to the genetic roots of autism. However, by no means this disputes or undermines other bio-social theories, such as the EP-M or Broken mirror reviewed yesterday, because these simply represent different levels of analysis. For example, we know that Down’s syndrome is caused by a an extra 21st chromosome. However, this only defines the syndrome. People with Down’s have specific deficits, such as intellectual impairment and delayed motor skills. But these impairment can be mapped to specific brain regions that have been compromised. So we have 3 levels of analysis in this case, the genetic anomaly is the cause the syndrome, which leads to compromised brain development, which leads to particular intellectual and motor difficulties. A similar process is likely in play in Autism. A series of genes anomalies are likely to be responsible for the disorder, leading to compromised brain development in specific regions (maybe mirror neuron system for example), leading in turn to social deficits.

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